In the deep-well drilling art, numerous tools are used which can be brought from a first into a second working state by a telescopic displacement of two parts situated one inside the other. Frequently, the first working state is that state in which the normal drilling activity is effected, while the second state serves, depending on the nature of the tool, for example to lock a rotatable part, to unlock a jarring device or, as a component of a jarring device, to release the relative movement of spindle and sleeve as well as to activate security devices and to separate parts from the drill string.
A locking device always prevents the telescopic displacement from being caused accidentally by the axial forces usual in normal operation. The superimposition of an axial overload is necessary for the unlocking, after which the tool can then be brought into the second state.
A locking device has been proposed heretofore which locks the free relative movement of a spindle in a sleeve until an axial overload is reached.
The locking elements are formed by cylindrical rolling bodies which are embedded, axially and radially located, in pockets of a spindle portion. Counter elements cooperating with these locking elements consist of a part which is displaceable axially at any time against a spring and a part which is also displaceable axially but which, in the locking state, bears against a stop and comprises three arms pivotable radially inwards.
Both types of counter element have, at the adjacent sides, oblique surfaces which can slide on one another with inward or outward pivoting of the arms on variation in the mutual axial position of the counter elements. The pivotable arms of the counter elements have further oblique surfaces which bear against the rolling bodies in the locking state so that when a force is imposed on the spindle portion, the rolling bodies roll on the oblique surfaces of the pivotable arms as a result of which these are forced apart and by means of their other oblique surfaces which are in engagement with the further parts of the counter elements, displace these parts axially against the spring. The free axial displacement is rendered possible for the spindle portion with the rolling bodies by the parting of the pivotable arms. Forces up to a few 10.sup.5 N may be necessary as forces usual in deep-well drilling tools to unlock a locking device because they must differ sufficiently from the normal axial forces. The wear of the locking device and the material loading should be as low as possible. In the device according to U.S. Pat. No. 2,678,805 a severe bending stress of the pivotable arms occurs with axial tensile loading and in addition, during the unlocking operation, friction between the oblique surfaces of the pivotable arms and the oblique surfaces of the counter element displaceable axially against the spring causes excess wear.
It is an object of the present invention to provide an improved locking device for a tool consisting of telescopically displaceable spindle and sleeve portions so that the wear and the material stressing with the usual operational forces is low so that constant, reproducible results are delivered even after repeated locking and unlocking cycles.